Cory's average score after 8 tests is 91%. if he gets a 78% on his 9th test what will his new average be?
how do i figure out this problem?

You should be able to multiply 91 by 8 to get the sum of the first 8 tests, then add the score on the 9th test. Then to get the average of the sum of the 9 tests you need to divide it by 9.
((91*8)+78)/9=89.555555555555 So, 90%

X=y+4 is the answe